This chapter provides a overview of the scientific principles of the brewing industry. Conversion of starch into simple sugars happens during mashing, and the changes during malting are limited to the breakdown of cell walls and the protein matrix in which the starch granules are embedded, but such modification of the grain is necessary for hydrolysis of the starch during mashing. It is now recognized that hops have an important antimicrobial, particularly antibacterial, effect, and it is presumed that the medieval brewers realized that hopped beers maintained their quality for longer periods of time than did beers with other flavorings. Formerly, the actively fermenting yeasts of the fermentation industries, both culture yeasts and common contaminant “wild yeasts,” were classified as different species of Saccharomyces. Most of these species are now classified officially by yeast taxonomists as a single species, S. cerevisiae, but still it is convenient in the brewing industry to distinguish the different types by their former specific names.Enterobacteria (including Obesumbacterium, the most important of that group in the brewery environment) cause turbidity and off-flavor and often produce indole, phenols, diacetyl, hydrogen sulfide, and dimethyl sulfide, but grow well in the early stages of fermentation until inhibited by the falling pH and increasing ethanol content. Megasphaera (cocci) and Pectinatus (rods) species are recently discovered strictly anaerobic gram-negative bacteria which form acetic, butyric, and propionic acids, hydrogen sulfide, dimethyl sulfide, and turbidity and have become troublesome only because of modern advances in maintaining very low dissolved oxygen levels in beer.

Theoretical progress of a typical brewery fermentation, showing changes in the population of S. cerevisiae and concentrations of fermentable sugar, amino nitrogen, and ethanol. The graph shows yeasts in suspension and the start of settling of cells from the beer at the end of fermentation. The time axis is not calibrated, since fermentation rates differ widely among breweries. Other variables are shown as percentages of the initial or final value, expressed as 100%.

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Figure 40.3

Theoretical progress of a typical brewery fermentation, showing changes in the population of S. cerevisiae and concentrations of fermentable sugar, amino nitrogen, and ethanol. The graph shows yeasts in suspension and the start of settling of cells from the beer at the end of fermentation. The time axis is not calibrated, since fermentation rates differ widely among breweries. Other variables are shown as percentages of the initial or final value, expressed as 100%.

CCFV. Vigorous circulation of fermenting wort is created by a central upward flow of CO2 bubbles and a downward flow in contact with the cooling jackets. Cooling of the cone section is optional, depending on whether the brewery stores settled yeast before the next fermentation.

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Figure 40.5

CCFV. Vigorous circulation of fermenting wort is created by a central upward flow of CO2 bubbles and a downward flow in contact with the cooling jackets. Cooling of the cone section is optional, depending on whether the brewery stores settled yeast before the next fermentation.

Identification of bacterial contaminants of the brewing industry. Bacillus, Micrococcus, and Streptococcus may be present but are unlikely to grow in beer, and Megasphera and Pectinatus grow only under strictly anaerobic conditions. HAc, acetic acid.

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Figure 40.6

Identification of bacterial contaminants of the brewing industry. Bacillus, Micrococcus, and Streptococcus may be present but are unlikely to grow in beer, and Megasphera and Pectinatus grow only under strictly anaerobic conditions. HAc, acetic acid.

Identification of common yeast contaminants of the brewing industry. All genera listed are teleomorphic, i.e., they form spores. Anamorphic (non-spore-forming) forms of Dekkera and Hanseniaspora are Brettanomyces and Kloeckera, respectively. The anamorph of all other genera listed is Candida. S. cerevisiae ferments glucose, sucrose, maltose, and raffinose but not lactose.

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Figure 40.7

Identification of common yeast contaminants of the brewing industry. All genera listed are teleomorphic, i.e., they form spores. Anamorphic (non-spore-forming) forms of Dekkera and Hanseniaspora are Brettanomyces and Kloeckera, respectively. The anamorph of all other genera listed is Candida. S. cerevisiae ferments glucose, sucrose, maltose, and raffinose but not lactose.